Fix IndexOnlyScan counter for heap fetches in parallel mode

The HeapFetches counter was using a simple value in IndexOnlyScanState,
which fails to propagate values from parallel workers; so the counts are
wrong when IndexOnlyScan runs in parallel.  Move it to Instrumentation,
like all the other counters.

While at it, change INSERT ON CONFLICT conflicting tuple counter to use
the new ntuples2 instead of nfiltered2, which is a blatant misuse.

Discussion: https://postgr.es/m/20180409215851.idwc75ct2bzi6tea@alvherre.pgsql

src/backend/commands/explain.c

@@ -1459,12 +1459,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				show_instrumentation_count("Rows Removed by Filter", 1,
 										   planstate, es);
 			if (es->analyze)
-			{
+				ExplainPropertyFloat("Heap Fetches", NULL,
-				long		heapFetches =
+									 planstate->instrument->ntuples2, 0, es);
-					((IndexOnlyScanState *) planstate)->ioss_HeapFetches;
-
-				ExplainPropertyInteger("Heap Fetches", NULL, heapFetches, es);
-			}
 			break;
 		case T_BitmapIndexScan:
 			show_scan_qual(((BitmapIndexScan *) plan)->indexqualorig,
@@ -3132,7 +3128,7 @@ show_modifytable_info(ModifyTableState *mtstate, List *ancestors,
 
 			/* count the number of source rows */
 			total = mtstate->mt_plans[0]->instrument->ntuples;
-			other_path = mtstate->ps.instrument->nfiltered2;
+			other_path = mtstate->ps.instrument->ntuples2;
 			insert_path = total - other_path;
 
 			ExplainPropertyFloat("Tuples Inserted", NULL,

src/backend/executor/instrument.c

@@ -156,6 +156,7 @@ InstrAggNode(Instrumentation *dst, Instrumentation *add)
 	dst->startup += add->startup;
 	dst->total += add->total;
 	dst->ntuples += add->ntuples;
+	dst->ntuples2 += add->ntuples2;
 	dst->nloops += add->nloops;
 	dst->nfiltered1 += add->nfiltered1;
 	dst->nfiltered2 += add->nfiltered2;

src/backend/executor/nodeIndexonlyscan.c

@@ -162,7 +162,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 			/*
 			 * Rats, we have to visit the heap to check visibility.
 			 */
-			node->ioss_HeapFetches++;
+			InstrCountTuples2(node, 1);
 			tuple = index_fetch_heap(scandesc);
 			if (tuple == NULL)
 				continue;		/* no visible tuple, try next index entry */
@@ -509,7 +509,6 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 	indexstate->ss.ps.plan = (Plan *) node;
 	indexstate->ss.ps.state = estate;
 	indexstate->ss.ps.ExecProcNode = ExecIndexOnlyScan;
-	indexstate->ioss_HeapFetches = 0;
 
 	/*
 	 * Miscellaneous initialization

src/backend/executor/nodeModifyTable.c

@@ -461,7 +461,7 @@ ExecInsert(ModifyTableState *mtstate,
 											 &conflictTid, planSlot, slot,
 											 estate, canSetTag, &returning))
 					{
-						InstrCountFiltered2(&mtstate->ps, 1);
+						InstrCountTuples2(&mtstate->ps, 1);
 						return returning;
 					}
 					else
@@ -476,7 +476,7 @@ ExecInsert(ModifyTableState *mtstate,
 					 */
 					Assert(onconflict == ONCONFLICT_NOTHING);
 					ExecCheckTIDVisible(estate, resultRelInfo, &conflictTid);
-					InstrCountFiltered2(&mtstate->ps, 1);
+					InstrCountTuples2(&mtstate->ps, 1);
 					return NULL;
 				}
 			}

src/include/executor/instrument.h

@@ -57,6 +57,7 @@ typedef struct Instrumentation
 	double		startup;		/* Total startup time (in seconds) */
 	double		total;			/* Total total time (in seconds) */
 	double		ntuples;		/* Total tuples produced */
+	double		ntuples2;		/* Secondary node-specific tuple counter */
 	double		nloops;			/* # of run cycles for this node */
 	double		nfiltered1;		/* # tuples removed by scanqual or joinqual OR
 								 * # tuples inserted by MERGE */

src/include/nodes/execnodes.h

@@ -1004,6 +1004,11 @@ typedef struct PlanState
 #define outerPlanState(node)		(((PlanState *)(node))->lefttree)
 
 /* Macros for inline access to certain instrumentation counters */
+#define InstrCountTuples2(node, delta) \
+	do { \
+		if (((PlanState *)(node))->instrument) \
+			((PlanState *)(node))->instrument->ntuples2 += (delta); \
+	} while (0)
 #define InstrCountFiltered1(node, delta) \
 	do { \
 		if (((PlanState *)(node))->instrument) \
@@ -1368,7 +1373,6 @@ typedef struct IndexScanState
  *		RelationDesc	   index relation descriptor
  *		ScanDesc		   index scan descriptor
  *		VMBuffer		   buffer in use for visibility map testing, if any
- *		HeapFetches		   number of tuples we were forced to fetch from heap
  *		ioss_PscanLen	   Size of parallel index-only scan descriptor
  * ----------------
  */
@@ -1387,7 +1391,6 @@ typedef struct IndexOnlyScanState
 	Relation	ioss_RelationDesc;
 	IndexScanDesc ioss_ScanDesc;
 	Buffer		ioss_VMBuffer;
-	long		ioss_HeapFetches;
 	Size		ioss_PscanLen;
 } IndexOnlyScanState;